Spanish teenager Carlos Alcaraz fulfilled his potential as a future Grand Slam champion and world number one by beating Casper Ruud in the US Open final to achieve both feats.

Alcaraz won 6-4 2-6 7-6 (7-1) 6-3 in his first major final.

The 19-year-old is the youngest men's Grand Slam champion since Rafael Nadal won the French Open in 2005.

Ruud, 23, would have become the new world number one if he had won, but has now lost both of his two major finals.

Instead it is Alcaraz who replaces Russia's Daniil Medvedev at the top, becoming the first teenager to climb to the summit in the 49-year history of the ATP rankings.

After hitting a routine forehand long on his first championship point, Alcaraz took his second with a service winner out wide and instantly fell flat on his back in celebration in New York.

Alcaraz, who saved two set points in the third which would have put Ruud ahead, ran up to his team in the stands and danced with them in a huddle, before returning to his seat where he was crying at the same time as smiling.

"This is something which I dreamt of since I was a kid, being number one in the world and a champion of a Grand Slam," said Alcaraz, who saved a match point against Jannik Sinner in the last eight to reach his first major semi-final.

"It is something I have worked very hard for. It is really, really special."